<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<script>
	alert(sum(10,10));//sum is not a function
	
	var sum=function(num1, num2){
			return num1+num2;
	};
	
	//js引擎会优先解析函数声明（在所有代码之前解析）
</script>
</head>

<body>
</body>
</html>
